Michelle Carter, 20, who encouraged her 18-year-old boyfriend — through text messages — to kill himself, was found guilty of involuntary manslaughter by a Massachusetts judge on Friday.

Conrad Roy killed himself on July 12, 2014, by inhaling carbon monoxide produced by a water pump in his truck. The teen — who had a history of mental illness and had previously attempted suicide — got out of the truck because he was "scared," but Carter texted him to "get back in," according to text messages the two exchanged during the course of their relationship.

Carter waived her right to a jury trial, leaving her fate to be decided by Judge Lawrence Moniz. On Friday, Moniz returned a guilty verdict.

Moniz said that Carter's actions constituted "wanton and reckless conduct" when she instructed Roy to get back in his truck despite knowing that it was a toxic environment "inconsistent with human life." He said that her conduct caused Roy's death.

Glenn C. Silva / AP

"She instructs Roy to get back in the truck knowing of all the feelings he has exchanged with her; his ambiguities, his fears, his concerns," Moniz said. "This court finds that by instructing Mr. Roy to get back in the truck constitutes wanton and reckless conduct by Ms. Carter, creating a situation where there is a high degree of likelihood that substantial harm would result to Mr. Roy."

Moniz said that Carter — in her text messages to friends — admitted that "she did nothing" to save Roy. He said that she did not call the police, or his family, despite knowing his location.

"She did not issue a simple additional instruction, 'Get out of the truck,'" Moniz said.

Moniz did not revoke Carter's bail and scheduled her sentencing for Aug. 3. She faces up to 20 years in prison for involuntary manslaughter.

Prosecutors had argued that through text messages and phone calls, Carter, 17 at the time, pressured Roy to kill himself, instructed him as to when and how to do it, assuaged his concerns over killing himself, and chastised him when he delayed doing so. They said that Carter used Roy as a "pawn in her sick game of life and death" and wanted to be "the grieving girlfriend" to gain her peers' attention and sympathy, which she always craved.

Court exhibits

Conrad Roy

Carter's defense team said that Roy was "suicidal" over a long period of time and that he "was on this path to take his own life for years."

Moniz said on Friday that it was "irrelevant" to the court whether Carter would have taken his life "at another time."

Carter's lawyers had also argued that since Carter was 30 miles away when Roy killed himself, she was not the cause of his death. They said his death was a suicide, not a homicide.

A controversial psychiatrist, Dr. Peter Breggin, testified Monday that Carter was "involuntarily intoxicated" by antidepressants, which made her "delusional" and "grandiose."

Breggin said Carter thought she was "doing a good thing" by encouraging Roy to kill himself.

Carter's lawyers had also said that she had her own "mental health issues" at the time of Roy's death and was "overwhelmed" by the relationship.

In a brief statement after the verdict, Roy's father said he was thankful to the judge and the prosecution team. "This has been a very tough time for our family and we’d like to process this verdict that we’re happy with," he said.

"Although we are very pleased with the verdict today, in reality there are no winners here today," Assistant District Attorney Katie Rayburn said at a press conference after the verdict.

"We fully understand that this was a unique case that dealt with a lot of important issues in our society today," Rayburn said. "But in the end, it was really about one young man and one young woman who were brought together by tragic circumstances."